Traditional metropolitan area communications services are based upon technologies such as asynchronous transfer mode (ATM), synchronous optical network (SONET), and Frame Relay technologies, which are optimized for voice communications services. With the increased use of the Internet as a communications medium, non-voice traffic (often referred to as data traffic) is becoming the most prevalent type of network traffic. To meet the increasing demand for data-centric communications services in metropolitan areas, new data-centric metropolitan area networks (MANs) are being built. These new MANs often utilize Ethernet at Layer 2 of the Open System Interconnection (OSI) model to connect nodes within the network (where the OSI model is defined by the International Standardization Organization (ISO)). Ethernet is a popular Layer 2 protocol for use in MANs because of its compatibility with the installed base of end users, its compatibility with the widely used Layer 3 Internet protocol (IP), because of its overall flexibility, and because it is relatively cheap to deploy when compared to other Layer 2technologies.
Although deploying Ethernet as the Layer 2 technology in MANs has many advantages, the end-user customers that are targeted to utilize MANs often desire advanced network services such as quality of service (QoS) guarantees, permanent virtual circuits (PVCs), Virtual Leased Lines (VLLs), and transparent LAN services (TLS). Many of these advanced services can be provided by a network that utilizes a Layer 2technology such as ATM, SONET, or Frame Relay. Ethernet, on the other hand, was not originally designed to provide advanced services and as a result, solutions to customer needs can be more difficult to implement in Ethernet-based networks.
One Ethernet technology that is presently utilized in MANs to provide advanced services to customers is VLAN technology. A VLAN is a group of network devices on different physical LAN segments that communicate with each other as if they were on the same physical LAN segment. The goal of VLAN technology is to make two network devices appear as if they are on the same logical LAN even though they are on different physical LANS.
From the perspective of a particular network switch, a VLAN is a broadcast domain. The broadcast domain can be used for packets, belonging to the VLAN, which are broadcast packets or packets whose destination MAC address has not been learned. A packet that is broadcast within a broadcast domain is sent to all ports in the broadcast domain except the port on which the packet was received. Typically, VLANs are configured within a multiport network node (e.g., a Layer 2 switch) by associating a particular VLAN identifier (ID) with a set of ports. The set of ports defines the broadcast domain of the VLAN within the multiport network node.
FIG. 1A depicts an example of a network that utilizes VLAN technology to connect customers between two service provider network nodes (network node A 102 and network node B 104). In the example of FIG. 1, the two locations of customer C1communicate with each other on VLAN 100 and the two locations of customer C2 communicate with each other on VLAN 200. With regard to network node A, the broadcast domain for VLAN 100 includes ports P1 and P3 and the broadcast domain for VLAN 200 includes ports P2 and P3. The broadcast domains for VLANs 100 and 200 at network node A are depicted in the VLAN table of FIG. 1B. In operation, a packet, which is a broadcast packet or a packet whose destination MAC address has not been learned, that is received at port P1 of network node A from customer C1 on VLAN 100 is broadcast to all ports in the VLAN except the port on which the packet was received. In this case, the packet is broadcast to port P3. From port P3, the packet is transmitted across the direct connection 106 to port P4 of network node B. At port P4 of network node B, a similar association is made for a broadcast packet or a packet whose destination MAC address has not been learned and the packet is broadcast to all ports in the broadcast domain except the port on which the packet was received. In this case, the packet is broadcast to port P5, where the packet eventually reaches customer C1. While FIG. 1A depicts a simplified network architecture in which the two service provider network nodes are directly connected, in many cases, service provider network nodes are separated by an intermediate network. For example, FIG. 2 depicts a network in which two service provider edge devices 202 and 204 are connected by an intermediate network 206 that may include multiple intermediate network nodes. Although traversing the intermediate network may involve multiple hops and many intermediate processing steps, the customers are only concerned that their traffic gets from one customer endpoint to the other. In particular, the customers want it to appear that their traffic is on one seamless LAN.
In order to provide VLAN services to customers that are connected by intermediate networks, service providers have employed “tunneling” technologies that essentially tunnel VLAN traffic through an intermediate network and deliver the VLAN traffic to a remote-end service provider edge device in the same form as it arrived at the near-end service provider edge device. FIG. 2 depicts an example transport tunnel 208 that exists between port P3 of service provider edge device A and port P4 of service provider edge device B. Because port P3 is connected to an intermediate network, the port may also support multiple additional transport tunnels 210 that connect to other service provider edge devices or to the same service provider edge device.
While establishing broadcast domains to connect remote customers is fairly straight forward when service provider network nodes are directly connected, the task becomes more difficult when service provider edge devices are connected through an intermediate network using tunneling technologies. In particular, the mere assigning of ports to a VLAN does not ensure that the traffic will be sent in the correct “tunnel” to the desired remote-end service provider edge device. The difficulty of the task is further increased as the number of different customers, service provider nodes, VLANs, and tunnels grows.
In view of the desire for VLAN-based services, what is needed is a technique that enables flexible deployment of VLANs across service provider networks that employ tunneling techniques.